In some centrifuges that continuously receive a stream of blood and provide separated streams of blood components, collection chambers have had three outlets, one for removing the heavy red blood cells at a radially outward position in the chamber, one for removing the lighter plasma at a radially inward position in the chamber, and one for removing the white blood cells and platelets of interest at the interface between the red cell layer and the plasma layer. The outlets are connected to respective pumps via tubing to a rotating seal or equivalent seal-less rotating tube structure.
In our U.S. Patent No. 4,094,461, which is hereby incorporated by reference, we disclosed a collection chamber in which a dam was placed behind the white cell outlet, to block flow past it of the white cell interface but permit flow of red cells and plasma; the plasma outlet was positioned behind the dam at generally the same radial position, as the interface outlet for the purpose of maintaining the interface position at the white cell outlet to provide efficient white cell removal. In a commercial embodiment of the device described in said patent, a four-channel rotating seal was used to connect the inlet tube and three collection tubes to three pumps.